Me and a few friends started to argue about magnets. Of course we know there are the laws of thermodynamics that basically say you cannot generate energy from nothing.
But what of magnets? If i stick a magnet to the fridge it must be generating at least enough energy to not fall down due to gravity.
Where is this energy coming from? Should it not like run out of energy sometime?
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It’s not generating any energy.
Just like if you hang a coat on the coat hanger, it isn’t generating energy by just sitting there.
You can think of magnets like of gravity: something in a magnetic field wants to move as close as possible to the magnetic pole.
Just like something in a gravitational field wants to get as close as possible to the center of that field.
And once two magnets are touching, (or as close as they can get) they are in the lowest energy state they can be, and it actually takes energy to seperate them again, and releases energy when they get closer. That’s why it’s hard to move apart magnets, but easy to move them closer.
The thing is that staying still does not consume energy(generally and macroscopically speaking).
Right now you are probably sitting on some chair. Gravity is pulling you toward the ground, but the chair is not expending any energy in keeping you up.
Sticking something to a vertical surface (the fridge) is not much different. Whether you use a magnet, of an adesive, you definitely have a force that is compensating gravity, but as long as the object is not moving energy has been used.
Looking at it from the equation side:
E = F * s
E = Energy expended;
F = Force;
s = distance moved.
The best analogy I can think of is a hill and gravity. If you have a generator on your bike just engage it and coast down the hill–> FREE ENERGY!
But now what? You’re at the bottom of the hill. How do you get more energy. No problem, ride the bike back up the hill. –> NOT SO FREE ENERGY.
In fact you’ve expended at least as much energy pushing yourself, the bike, and the generator back up the hill. Gravity is a force, and you can get energy from things being pulled by gravity (think hydroelectric dams), but it only works while the thing is going down. Once it’s down, the only way to get it back up is to put energy into it. Hydroelectric dams using falling water for power, but they’re basically indirect solar energy plants because the sun provided the energy to evaporate the water so it could end up raining onto the higher elevations.
Now to magnets. They provide the force, like gravity, and you can get energy by the motion of two magnets either being pulled together, or repelling each other. Just like gravity however, it only works once, then you either have to magnets stuck together or two magnets that have pushed each other apart. You need to put energy in to get them back into their original position.
The magnet on the fridge is producing a force, but without motion, there is no energy being created or consumed. The important fact here is that force and energy are two different things.
> it must be generating at least enough energy to not fall down
This is incorrect, in the same way that a stone doesn’t need to expend energy to stay put on the floor, or a picture doesn’t need to use energy to stay hanging on a wall.
Generally, energy is expended to *move* against a force. Though of course that principle gets difficult when thinking of eg flying objects (there is lots of air being moved around even for something hovering) or electricity (electric charges and fields are moving), but static magnetism, once it has reached a steady state, doesn’t use energy up. It’s a bit difficult to ELI5 why, but essentially all the atoms in the magnet want to point the same direction, and as a result make a magnetic field that also influences atoms in the fridge to point in the same direction, which in turn creates its own magnetic field in the magnet. This interaction pulls the magnet and the fridge together, such that the friction between them is higher than the weight of the magnet and it stays in place. The “atoms lining up one way” is an elastic process, kind of like they’re all little springs being stretched or twisted a little bit, so they can stay stretched quite happily and spring back together after the magnet and fridge are separated.
You are mixing 2 things together… Energy and force
If you glue brick to your ceiling, the force of glue supports it… But there is no energy being generated
Laws of conservation, not thermodynamics.
They apply to magnets too. There’s no energy being exerted when a magnet sticks to a fridge. No useful work can be extracted from it without putting energy into the system. Sure, if you wanted to hold something onto the fridge and fight gravity, it would take energy, but a magnet is just sitting there.
Look at your chair. It’s on the ground. Holy shit, how can it do that, it just stays there! Because Earth has gravity. And that’s useful, but we can’t extract energy directly from the chair being in the floor. Same with magnets, even if they’re overcoming gravity.
It’s a force, not energy. Your chair has a downward force on it. But unless it moves, there’s no energy there. If it does fall, like on a teeter tauter or something, that IS potential energy. But then you have to lift up the chair again and put in energy to do it again. Same with magnetic force.
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